1 files changed, 77 insertions, 0 deletions
diff --git a/third_party/rust/unreachable/src/lib.rs b/third_party/rust/unreachable/src/lib.rs
new file mode 100644
index 0000000000..bb9b334312
--- /dev/null
+++ b/third_party/rust/unreachable/src/lib.rs
@@ -0,0 +1,77 @@
+#![cfg_attr(test, deny(warnings))]
+#![deny(missing_docs)]
+
+//! # unreachable
+//!
+//! An unreachable code optimization hint in stable rust, and some useful
+//! extension traits for `Option` and `Result`.
+//!
+
+#![no_std]
+
+extern crate void;
+
+use core::mem;
+
+/// Hint to the optimizer that any code path which calls this function is
+/// statically unreachable and can be removed.
+///
+/// Calling this function in reachable code invokes undefined behavior. Be
+/// very, very sure this is what you want; often, a simple `panic!` is more
+/// suitable.
+#[inline]
+pub unsafe fn unreachable() -> ! {
+    let x: &void::Void = mem::transmute(1usize);
+    void::unreachable(*x)
+}
+
+/// An extension trait for `Option<T>` providing unchecked unwrapping methods.
+pub trait UncheckedOptionExt<T> {
+    /// Get the value out of this Option without checking for None.
+    unsafe fn unchecked_unwrap(self) -> T;
+
+    /// Assert that this Option is a None to the optimizer.
+    unsafe fn unchecked_unwrap_none(self);
+}
+
+/// An extension trait for `Result<T, E>` providing unchecked unwrapping methods.
+pub trait UncheckedResultExt<T, E> {
+    /// Get the value out of this Result without checking for Err.
+    unsafe fn unchecked_unwrap_ok(self) -> T;
+
+    /// Get the error out of this Result without checking for Ok.
+    unsafe fn unchecked_unwrap_err(self) -> E;
+}
+
+impl<T> UncheckedOptionExt<T> for Option<T> {
+    unsafe fn unchecked_unwrap(self) -> T {
+        match self {
+            Some(x) => x,
+            None => unreachable()
+        }
+    }
+
+    unsafe fn unchecked_unwrap_none(self) {
+        match self {
+            Some(_) => unreachable(),
+            None => ()
+        }
+    }
+}
+
+impl<T, E> UncheckedResultExt<T, E> for Result<T, E> {
+    unsafe fn unchecked_unwrap_ok(self) -> T {
+        match self {
+            Ok(x) => x,
+            Err(_) => unreachable()
+        }
+    }
+
+    unsafe fn unchecked_unwrap_err(self) -> E {
+        match self {
+            Ok(_) => unreachable(),
+            Err(e) => e
+        }
+    }
+}
+